1. Field of the Invention
The invention relates to a motive power output device, and a vehicle equipped with the device as well as a control method for the motive power output device.
2. Description of the Related Art
There has been proposed a motive power output device which includes an engine, a planetary gear whose carrier is connected to a crankshaft of the engine, and whose ring gear is connected to a driving shaft linked to an axle shaft, a motor MG1 connected to a sun gear of the planetary gear, and a motor MG2 connected to the driving shaft, and which controls the engine and two electric motors MG1, MG2 so as to output a required torque that is required for the traveling of the vehicle while operating the engine on a steady travel-time operation line within a range of restriction of the charging and discharging of a battery (e.g., see Japanese Patent Application Publication No. 2000-115913 (JP-A-2000-115913)). This device sets a target rotation speed and a target torque as points of operation of the engine, and sets a target torque of the motor MG1 so that the engine rotates at the target rotation speed, and sets and controls the torque of the motor MG1 by restricting the target torque by using a maximum restriction torque value obtained from the input/output restriction which is a maximum electric power that can be charged into or discharged from the battery.
However, in the foregoing motive power output device, when the required torque sharply changes, it sometimes becomes difficult to drive the two motors at a proper drive point. When the torque from a motor is to be sharply changed, it is often the case that the maximum amount of change in the torque per unit time is pre-set so as to avoid overcurrent flowing to an inverter that drives the motor. Therefore, when the torque of the motor is to be changed, the maximum amount of change in the torque needs to be taken into account in addition to considering the rated value of the motor, in order to more properly drive the motor. In the device equipped with a voltage boost circuit that boosts the voltage of the electric power from a battery and supplies the boosted power to the motors, the state of operation of the voltage boost circuit varies between when the voltage from the battery is directly supplied to the motor side without operating the voltage boost circuit at all and when a voltage higher than the voltage from the battery is supplied to the motor side via the voltage boost circuit. Therefore, the amount of change in the current flowing through the inverter per unit time varies, and the maximum amount of change in the torque of the motor per unit time also varies.